Remove empty non-virtual destructors or mark them =default when non-public

These add no value but can make a class non-trivially copyable. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234688 91177308-0d34-0410-b5e6-96231b3b80d8

lib/TableGen/TGLexer.h

@@ -87,8 +87,7 @@ private:
 
 public:
   TGLexer(SourceMgr &SrcMgr);
-  ~TGLexer() {}
-  
+
   tgtok::TokKind Lex() {
     return CurCode = LexToken();
   }